Off road work vehicles in the agricultural, mining and construction fields, such as tractors, and the like, have traditionally operated with manual steering. Improvements in control system design and related position sensing technology, such as global positioning systems (GPS), including differential correction systems, as well as real time kinematic (RTK) satellite navigation have led to an increase in the use of automatic guidance control systems for these vehicles. The combination of improved navigation input signals precisely identifying vehicle position and speed with sophisticated on board vehicle electronic control systems allows for automatic guidance systems capable of steering the vehicle with a high degree of accuracy when traversing terrain.
To provide this control, the prior art teaches using satellite positioning information by an onboard vehicle navigation control system to accurately determine and control a vehicle's position while operating in a field. A preplanned route, based on information previously known about the terrain of the field, or a control system generated route may be used. The control methods are well known in the art, and may involve multiple position transmitters or receivers, with various signals used to derive vehicle location, elevation, direction of travel or heading, and speed.
The task of precision guidance of an agricultural vehicle involves not only accurately determining vehicle position in a field, but also defining an efficient swath pattern or array of swath lines to be followed by the vehicle that will, in conjunction with the swath width of an element associated with the vehicle, create an overall swath pattern that efficiently and effectively covers the crop area of a field. The pattern must be located and oriented on the field, and the physical characteristics and limitations of the vehicle and coupled implement must be identified and provided to the navigation system. Implement or header width, location of the implement or header with respect to the vehicle, and limitations on the vehicle and associated implement movement, such as minimum turning radius, must also be considered. With this information it is possible to define an array or series of swath lines for the vehicle to travel in an attempt to cover all cultivatable portions of a field without unnecessary skips or overlaps.
Calculating the series of swath lines needed to cover an area without substantial skips or overlaps is relatively straightforward when straight lines can be used; however, not all fields can be covered in this manner. In some fields it may be desirable to use a spiral swath pattern in which the swath lines require a variation in curvature along at least some portion of its length. Such conditions preclude a complete reliance on geometrically predefined swath lines, such as straight lines or constant radius curves. In order to provide generally equally spaced swath lines for a spiral swath pattern, each adjacent swath line must change slightly compared to the prior swath line as the vehicle traverses field.
Vehicle navigation systems typically must be able to store and retrieve swath path information as well as determine new adjacent swath paths from a baseline swath path or create new swath paths from defined starting and ending positions. The number of swath lines to be stored and/or determined increases as the size of the field increases. Presently known systems for generating spiral swath patterns require a significant number of positional data points to fully define the swath lines between starting and ending points compared to using only starting and ending position points to create straight-line paths. The computation time and memory storage required for generating and traversing a spiral swath pattern are often drawbacks to these systems. Thus the size and arrangement of some fields is such that generating and/or storing a spiral swath pattern according to presently known methods is both inconvenient and inefficient because of the computation time and memory requirements, especially if the field is large and the system boundary is known and can be described by a convex polygon.
In addition, presently known systems typically generate swath lines as a function of a baseline swath line. The radius of curvature of every curved portion of each of the generated swath lines must then be computed and compared to the minimum turning radius of the vehicle. If the radius of curvature of the generated swath line is too small, the generated swath line must be regenerated for use by the vehicle. Often this computation and regeneration is made during operation of the vehicle in the field resulting in increased computation and memory requirements.
What is sought is a system and method to generate spiral swath patterns for a convex polygon shaped field which overcomes at least one of the problems, shortcomings, or disadvantages set forth above.